Microelectromechanical systems (“MEMS,” also referred to as “MEMS devices”) are a specific type of integrated circuit used in a growing number of applications. For example, MEMS currently are implemented as microphones in mobile telephones and tablets, gyroscopes to detect pitch angles of airplanes, and accelerometers to selectively deploy air bags in automobiles. In simplified terms, such MEMS devices typically have a fragile movable structure suspended above a substrate, and associated circuitry (on chip or off chip) that both senses movement of the suspended structure and delivers the sensed movement data to one or more external devices (e.g., an external computer). The external device processes the sensed data to calculate the property being measured (e.g., pitch angle or acceleration).
Micromachining processes often form MEMS devices using additive and subtractive processes. For example, during fabrication, some processes deposit sacrificial material under the movable structure. To release the movable structure (i.e., so that it may be in a movable state), the sacrificial material under that movable structure must be removed. Although this process has been commonplace for years, removal of the sacrificial material can present a number of fabrication and performance problems.